MOLLGAARD S RETICULUM 



327 



adjacent walls. This appearance is observed of course only in 

 freshly frozen preparations, not after their fixation, and is men- 

 tioned only to insure a more correct association between the 

 appearances of the aqueous and less aqueous portions of the 

 preparations. 



The appearance of ice in animal tissues seems to have been 

 quite neglected, but its appearance in plant tissues has been 

 variously noted by Miiller-Thurgau f'80 and '86), Fischer fTl), 

 Wiegand ('11), and others. The details of ice formation however 

 need not be entered into here; for such details, with physico- 

 chemical explanation, are given at length by Quincke ('05). 



:zt=^.C^ \ 



Fig. 1 This figure is a reproduction of Molisch's ('97) figure 6, with a reduc- 

 tion of one-sixth. It represents the reticulum observed in a thin fihii of starch- 

 paste, first frozen and then permitted to thaw out. 



The appearance of frozen egg-albumen is also instructive. 

 Depending on the conditions of the freezing, many variations 

 occur, but in general the appearance is one of a variable network 

 or reticulum the meshes of which are filled with ice. Disregard- 

 ing the variations, the network is not unlike that figured by 

 Molisch ('97) for frozen starch-paste with subsequent thawing 

 (fig. 1). Small air-bubbles are usually present, and intermingled 

 with the reticulum, if the temperature employed be low enough, 

 many small clefts occur. 



It should be remarked that Molisch ('97 and '11) has made 

 extensive observations on the action of freezing on many sub- 

 stances, solutions, and emulsions, colloidal and otherwise. From 



